Answer
General equation is: $a_n=7+(-4)(n-1)$; and $-69$
Work Step by Step
Formula to calculate the nth term of an arithmetic sequence is: $a_n=a_1+d(n-1)$
Here, $a_1: $ First term and $d=$ common difference
Since, we have $a_1=7$
Then, our General equation is: $a_n=7+(-4)(n-1)$
$a_{20}=7+(-4)(20-1)=7-76=-69$
